In ultrasound imaging systems, images of a tissue region are created by transmitting one or more acoustic pulses into the body from a transducer. Reflected echo signals that are created in response to the pulses are detected by the same or a different transducer. The echo signals cause the transducer elements to produce electronic signals that are analyzed by the ultrasound system in order to create a map of some characteristic of the echo signals such as their amplitude, power, phase or frequency shift etc. The map therefore can be displayed to a user as an image of the tissue.
Most imaging ultrasound transducers have a number of individual piezoelectric transducer elements that are typically arranged in a linear, curved, concentric or two-dimensional array. In some cases, the array may be one element wide such as 128×1 elements. In other cases, higher dimensional arrays such as 128×2, 128×4 . . . 128×128 elements are used.
In order to accurately determine a characteristic of an echo signal at a particular location or point of interest (“POI”) in the body, the signals from multiple transducer elements are analyzed. However, the acoustic echo signals generated at any given POI reach each of the transducer elements at slightly different times. Therefore, the ultrasound system performs a task of beamforming that aligns the received echo signals from the various transducer elements so that the echo signals originating from the same POI can be analyzed. Beamforming typically involves storing the signals from each transducer element by at least an amount of time equal to the time it takes for an acoustic signal to reach the transducer elements that are the farthest from a POI. Some systems store signals from an entire region of interest. The stored signals from a number of the transducer elements are then delayed, aligned, weighted and combined to determine a characteristic of an echo signal at a particular POI.
Beamforming is generally the most computationally intensive task that is performed by programmable or special purpose processors (e.g. DSPs) within an imaging system. The beamforming process therefore contributes significantly to the processing time required to produce images of tissue in the body. The overhead increases the time required to produce images as well as the cost and complexity of the processing components of the imaging system and the electrical power required to run those components.